A conventional PGA package socket comprises a base housing having a plurality of terminals arranged in the form of a grid and a slide plate having a corresponding plurality of through holes made in the form of a grid. The slide plate is laid on the base housing, and it is movable between the first position in which the lead pins of a PGA package are permitted to be inserted in the terminal mounts in the base housing without substantial force applied to the PGA package and the second position in which the lead pins are put in contact with the terminals mounted in the base housing.
One example of means for moving the slide plate on the base housing comprises a cam axle extending on the rear lateral edge of the base housing and a handle positioned on one side of the base housing, and operatively connected to the cam axle (see Japan Patent Application Laid-Open Nos. 7-142134, 4-319277, 56-125861 and 11-185914). Another example of slide plate driving means comprises a cam member passing through the base housing and the slide plate. The cam member has a recess made in its head for accommodating a screwdriver or a small-sized hexagonal socket wrench. Using such a tool in place of the handle can move the cam member.
Referring to FIG. 7(a), a PGA package socket has a cam member 10 passing through its base housing and slide plate. The cam member 10 is circular, and its circular outer circumference 12 is put partly in contact with the opposite lateral sides of the cam hole 18 made in the slide plate 11.
The pivot axle (broken lines) 13 of the cam member 10 has its center 13a offset from the center 12a of the circular outer circumference 12 of the cam member 10. A hexagonal socket wrench is inserted in the hexagonal hole 14 of the head of the cam member 10 to be rotated in the direction indicated by arrow A. Then, the situation as shown in FIG. 7(b) is brought about, where the slide plate 11 is moved in the direction as indicated by arrow B.
Specifically the cam member 10 pushes the slide plate 11 by applying the pushing force X to the slide plate 11. When the radial protrusion 15 abuts on the retainer 16, rotation of the cam member 10 stops. In this position the lead pins of the PGA package are put in contact with the terminals of the socket, so that the kickback force Y may be caused from the resultant resilient force of all lead pins as a counter force to the pushing force X (see FIG. 7(b)). The kickback Y increases with the increase of the number of the terminals or the lead pins of the PGA package.
As shown in FIG. 7(b), the pushing force X opposes the kickback Y. For accidental reasons these forces fail to oppose each other, so that the cam member 10 may be rotated in the direction indicated by arrow C. As a result the electric connection between the lead pins of the PGA package and the terminals of the socket is loosened.
In the hope of solving this problem, as shown in FIG. 8(a), a cam member 20 has a flat 22 chamfered on one side, on which side the cam member 20 pushes the slide plate 21, and is locked in this position. The cam member 20 is not circular, allowing a significant gap to appear between the outer circumference of the cam member 20 and one lateral side of the cam hole 23 in the slide plate 21. Such a significant gap is apt to cause an adverse effect on the function of permitting the force-free insertion of the lead pins of a PGA package in the terminal mounts, since the side plate can move upwardly or downwardly. Still disadvantageously, the curve-to-flat transient or angular corner 22a of the cam member 20 is apt to be badly loaded when the cam member 20 is made to rotate from the unlocking position (FIG. 8(b)) to the locking position (FIG. 8(a)), and the angular corner 22a is apt to be deformed. It means the reduction of lifespan of the cam.